jQuery(document).ready(function ($) {
  // browser window scroll (in pixels) after which the "back to top" link is shown
  var offset = 300,
    //browser window scroll (in pixels) after which the "back to top" link opacity is reduced
    offset_opacity = 1200,
    //duration of the top scrolling animation (in ms)
    scroll_top_duration = 400,
    //grab the "back to top" link
    $back_to_top = $('.cd-top')

  //hide or show the "back to top" link
  $(window).scroll(function () {
    $(this).scrollTop() > offset ? $back_to_top.addClass('cd-is-visible') : $back_to_top.removeClass('cd-is-visible cd-fade-out')
    if ($(this).scrollTop() > offset_opacity) {
      $back_to_top.addClass('cd-fade-out')
    }
  })

  //smooth scroll to top
  $back_to_top.on('click', function (event) {
    event.preventDefault()
    $('body,html').animate(
      {
        scrollTop: 0
      },
      scroll_top_duration
    )
  })
})
